1. Field of the Invention
The present invention relates to a magnetic film permitting an increase in the saturation magnetic flux density Bs of a NiFe alloy used as, for example, a core material of a thin film magnetic head, as compared with a conventional value, and having excellent other soft magnetic properties and film properties, and a method of producing the magnetic film. The present invention also relates to a thin film magnetic head using the magnetic film, and a method of manufacturing the thin film magnetic head.
2. Description of the Related Art
In a planar magnetic device such as a thin film magnetic head, a thin film inductor, or the like, a NiFe alloy (Permalloy) is frequently used for a portion made of magnetic a material.
The NiFe alloy has relatively excellent soft magnetic properties, and can easily be plated, and thus the NiFe alloy is one of magnetic materials frequently used.
The NiFe alloy is conventionally plated by electroplating with a DC current. The Fe composition ratio is generally about 45% by mass to 55% by mass. The NiFe alloy having this composition has a saturation magnetic flux density Bs of about 1.5 T (Tesla).
However, in order to improve a recording density in future, it is demanded to further increase the saturation magnetic flux density Bs of the NiFe alloy.
Therefore, the inventors used an electroplating method using a pulsed current in place of a conventional electroplating method using a DC current. As a result, the inventors could increase the Fe composition ratio X of the NiFe alloy as compared with a conventional alloy, and succeeded in increasing the saturation magnetic flux density mainly depending upon the Fe composition ratio X. Specifically, the inventors succeeded in greatly increasing the saturation magnetic flux density Bs to about 1.9 T. A NiFe alloy film formed by an electroplating method using a pulsed current, and a method of producing the same have already been applied for a patent as U.S. patent application Ser. No. 09/599,349.
According to U.S. patent application Ser. No. 09/599,349, a soft magnetic film of an NiFe alloy having a Fe composition ratio X of 60% by mass to 75% by mass, and an average crystal grain diameter of 105 xc3x85 or less can be produced by an electroplating method using a pulsed current.
However, the soft magnetic film has the problem in which the saturation magnetic flux density Bs cannot be increased to 1.9 T or more.
The plating bath composition used for producing the soft magnetic film has a Ni ion concentration of about 40 g/l. Although the Fe composition ratio of the NiFe alloy can be possibly increased by increasing the Fe ion concentration of the plating bath, it was found by actual experiment that the Fe composition ratio cannot be increased to 75% by mass or more. Even if the Fe composition ratio can be increased to 75% by mass or more, crystallinity deteriorates to fail to form a dense crystal, thereby failing to improve the saturation magnetic flux density Bs and deteriorating other film properties such as coercive force, surface roughness, etc.
Accordingly, the present invention has been achieved for solving the above problem of conventional NiFe alloys, and an object of the present invention is to provide a soft magnetic film permitting an increase in the saturation magnetic flux density Bs of a NiFe alloy, and having excellent other soft magnetic properties and film properties.
Another object of the present invention is to provide a thin film magnetic head using a soft magnetic film having a high saturation magnetic flux density Bs of 1.9 T or more so that it can comply with increases in recording density and frequency in future.
A further object of the present invention is to provide a method of manufacturing a thin film magnetic head which is capable of increasing the Fe content in a NiFe alloy by appropriately controlling a plating bath composition, and forming a crystal having a larger crystal grain diameter and higher density than conventional NiFe alloys.
A soft magnetic film of the present invention has a composition represented by the formula Ni1-XFeX wherein the Fe composition ratio X is 76% by mass to 90% by mass.
In the present invention, the soft magnetic film preferably has an average crystal grain diameter of 150 xc3x85 to 175 xc3x85.
In a NiFe alloy according to a first embodiment of the present invention, only the Fe composition ratio X is defined. The saturation magnetic flux density Bs mainly depends upon the Fe composition ratio X, and increases as the Fe composition ratio X increases. The possible reason for this is that crystallization is appropriately promoted by increasing the Fe composition ratio X to form a dense crystal. However, with the Fe composition ratio X of a certain value or more, crystallization is conversely inhibited to fail to form a dense crystal, possibly decreasing Bs.
A production method of the present invention described below is capable of setting the Fe content of the NiFe alloy to 76% by mass to 90% by mass by appropriately controlling the composition of a plating bath. Therefore, the saturation magnetic flux density Bs of the NiFe alloy can be increased to 1.95 T or more. Also, coercive force Hc can be suppressed to 553 (A/m) or less.
A soft magnetic film of the present invention has a composition represented by the formula Ni1-XFeX wherein the average crystal grain diameter is 130 xc3x85 to 175 xc3x85, and the Fe composition ratio X is in the range of 70% by mass to 90% by mass.
In a NiFe alloy according to a second embodiment of the present invention, the Fe composition ratio and the average crystal grain diameter of the NiFe alloy are defined.
As described above, the saturation magnetic flux density Bs mainly depends upon the Fe composition ratio X, but a higher saturation magnetic flux density Bs can be stably obtained by further setting the average crystal grain diameter in an appropriate range.
In U.S. patent application Ser. No. 09/599,349, now U.S. Pat. No. 6,449,122, the Fe composition ratio X can be increased to 75% by mass which lies in the range of the Fe composition ratio X of the NiFe alloy according to the second embodiment of the present invention.
Although the range of the Fe composition ratio X of the present invention partially overlaps with that of U.S. patent application Ser. No. 09/599,349, now U.S. Pat. No. 6,449,122, the present invention greatly differs from U.S. patent application Ser. No. 09/599,349, now U.S. Pat. No. 6,449,122, in the crystal grain diameter. Namely, in the present invention, the crystal grain diameter is defined to 130 xc3x85 or more, while in U.S. patent application Ser. No. 09/599,349 (U.S. Pat. No. 6,449,122), the crystal grain diameter is defined to 105 xc3x85 or less.
In the present invention, crystallization is possibly appropriately promoted to increase the crystal grain diameter, forming a dense crystal, as compared with the NiFe alloy of U.S. patent application Ser. No. 09/599,349 (U.S. Pat. No. 6,449,122). As a result, in the present invention, the saturation magnetic flux density Bs of the NiFe alloy can be increased to 1.9 T or more, succeeding in effectively increasing the saturation magnetic flux density Bs.
In the present invention, coercive force can be suppressed to 553 (A/m) or less. The coercive force Hc possibly increases as the crystal grain diameter increases. However, in the present invention, the coercive force Hc little increases even when the crystal grain diameter increases, and the coercive force Hc of 553 (A/m) or less is a low value sufficiently used, for example, for a core material of a thin film magnetic head.
The possible reason why the coercive force Hc can be kept down even when the crystal grain diameter increases is that a crystal is densely grown. When the crystal is densely formed, the surface roughness of a film plane can be decreased, and in the present invention, the center line average roughness Ra of the film plane can be suppressed to 10 nm or less. In the present invention, the center line average roughness Ra is preferably 7 nm or less.
In the present invention, the Fe composition ratio X is preferably 72.5% by mass or more. This can increase the saturation magnetic flux density Bs of the NiFe alloy to 1.95 T or more.
Also, the average crystal grain diameter is preferably 150 xc3x85 or more. This can securely increase the saturation magnetic flux density Bs of the NiFe alloy to 1.95 T or more.
In the present invention, the Fe composition ratio X is preferably 78% by mass to 85% by mass. This can increase the saturation magnetic flux density Bs of the NiFe alloy to 2.0 T or more.
In the present invention, the soft magnetic film is preferably formed by plating. By forming the soft magnetic film by plating, the thickness can be relatively freely changed to form the soft magnetic thick film.
A method of producing a soft magnetic film of the present invention comprises plating a NiFe alloy by an electroplating method using a pulsed current, wherein the Ni ion concentration of a plating bath is 6.6 g/l to 20 g/l, and the ratio of the Fe ion concentration to the Ni ion concentration is 0.15 to 0.36.
As described above, in the present invention, the NiFe alloy is plated by the electroplating method using the pulsed current. In the electroplating method using the pulsed current, for example, a current control device is repeatedly turned on and off to provide a time to pass the current, and a blank time to pass no current. By providing the time to pass no current, the NiFe alloy film can be slowly formed by plating to reduce the deviation of the current density distribution at the time of plating, as compared with an electroplating method using a DC current. By the electroplating method using the pulsed current, the Fe content of the soft magnetic film can easily be controlled to increase the Fe content of the film, as compared with the electroplating method with the DC current.
In the present invention, the Ni ion concentration of the plating bath is set to 6.6 g/l to 20 g/l. In a conventional method, the Ni ion concentration is about 40 g/l, while in the present invention, the Ni ion concentration is lower than that value. As a result, the amount of Ni ions of the plating solution, which contact the surface of a cathode (the plated side) during deposition, can be decreased, thereby increasing the Fe content of the NiFe alloy due to the improved agitation effect.
As described above, in the present invention, the ratio of the Fe ion concentration to the Ni ion concentration is set to 0.15 to 0.36. Namely, in the present invention, not only the Ni ion concentration but also the Fe ion/Ni ion ratio is defined to increase crystallinity, permitting the formation of a dense crystal. In the present invention, the Ni ion concentration is decreased, and the concentration ratio is set to the above value, increasing the Fe content and the crystal grain diameter of the NiFe alloy. However, since the dense crystal can be formed, a high saturation magnetic flux density Bs can be stably obtained, and coercive force Hx can be decreased. Furthermore, surface roughness can be decreased, and membrane stress can also be decreased.
By using the above-described plating bath, the NiFe alloy film having a Fe composition ratio of 76% by mass to 90% by mass, or a Fe composition ratio of 70% by mass to 90% by mass, and an average crystal grain diameter of 130 xc3x85 to 175 xc3x85 can be produced with high reproducibility.
In the present invention, preferably, the Ni ion concentration is 10 g/l or more, and the Fe ion concentration/Ni ion concentration ratio is 0.2 to 0.35.
In the present invention, preferably, the Ni ion concentration is 10 g/l or less, and the Fe ion concentration/Ni ion concentration ratio is 0.15 to 0.36.
In the present invention, saccharin sodium is preferably mixed with the plating bath of the NiFe alloy. Saccharin sodium (C6H4CONNaSO2) has the function as a stress relaxant, and the membrane stress of the NiFe alloy can be decreased by mixing saccharin sodium.
In the present invention, 2-butine-1,4-diol is preferably mixed with the plating bath. This can suppress coarsening of the crystal grains of the NiFe alloy plated to decrease the crystal grain diameter, thereby causing less voids between the crystal grains and suppressing surface roughness of the film plane. By suppressing surface roughness, the coercive force Hc can be decreased.
In the present invention, sodium 2-ethylhexyl sulfate is preferably mixed with the plating bath. Therefore, hydrogen produced in the plating bath is removed by sodium 2-ethylhexyl sulfate serving as a surfactant to prevent adhesion of hydrogen to the plated film, suppressing surface roughness.
Although sodium lauryl sulfate may be used in place of sodium 2-ethylhexyl sulfate, sodium 2-ethylhexyl sulfate produces less bubbles in mixing with the plating bath, and thus a large amount of sodium 2-ethylhexyl sulfate can be mixed with the plating bath, permitting the appropriate removal of hydrogen. By adding sodium 2-ethylhexyl sulfate, the membrane stress of the NiFe alloy can also be decreased.
A thin film magnetic head of the present invention comprises a lower core layer made of a magnetic material, an upper core layer formed on the lower core layer with a magnetic gap provided therebetween, and a coil layer for supplying a recording magnetic field to both core layers, wherein at least one of the core layers comprises a soft magnetic film represented by the composition formula Ni1-XFeX, and having a Fe composition ratio X of 76% by mass to 90% by mass.
In the present invention, the thin film magnetic head preferably further comprises a lower pole layer formed to protrude above the lower core layer at a surface facing a recording medium, wherein the lower pole layer comprises the soft magnetic film.
A thin film magnetic head of the present invention comprises a lower core layer, an upper core layer, and a pole portion located between the lower core layer and the upper core layer and having a width dimension in the track width direction, which is defined to be shorter than the lower core layer and the upper core layer, wherein the pole portion comprises a lower pole layer continued from the lower core layer, an upper pole layer continued from the upper core layer, and a gap layer positioned between the lower pole layer and the upper pole layer, or an upper pole layer continued from the upper core layer and a gap layer positioned between the upper pole layer and the lower core layer, and wherein the upper pole layer and/or the lower pole layer comprises a soft magnetic film represented by the composition formula Ni1-XFeX, and having a Fe composition ratio X of 76% by mass to 90% by mass.
In the present invention, preferably, the upper pole layer comprises the soft magnetic film, and the upper core layer formed on the upper pole layer comprises a soft magnetic film having a lower saturation magnetic flux density Bs than the upper pole layer.
In the present invention, preferably, each of the core layers comprises at least a portion in contact with the magnetic gap, which comprises at least two magnetic layers, or each of the pole layers comprises at least two magnetic layers, the magnetic layer in contact with the magnetic gap comprising the soft magnetic film.
In the present invention, the magnetic layer other than the magnetic layer in contact with the magnetic gap comprises a soft magnetic film having a lower saturation magnetic flux density Bs than the magnetic layer in contact with the magnetic gap.
In the present invention, the soft magnetic film preferably has an average crystal grain diameter of 150 xc3x85 to 175 xc3x85.
The soft magnetic film used for the core layers and the pole layers of the thin film magnetic head of the present invention is represented by the composition formula Ni1-XFeX wherein the Fe composition ratio X is 76% by mass to 90% by mass.
In the NiFe alloy according to the first embodiment of the present invention, only the Fe composition ratio X of the NiFe alloy is defined. The saturation magnetic flux density Bs mainly depends upon the Fe composition ratio X, and increases as the Fe composition ratio X increases. The possible reason for this is that crystallization is appropriately promoted by increasing the Fe composition ratio X to densely form a crystal. However, with a Fe composition ratio of a certain value or more, crystallization is conversely inhibited to fail to form a dense crystal, thereby possibly decreasing the Bs.
In a production method of the present invention described below, the composition of a plating bath is appropriately controlled to set the Fe content of the NiFe alloy to 76% by mass to 90% by mass. This can increase the saturation magnetic flux density Bs of the NiFe alloy to 1.95 T or more. Also, coercive force Hc can be suppressed to 553 (A/m) or less.
By using the NiFe alloy for the core layers and the pole layers of the thin film magnetic head, a magnetic flux can be concentrated in the vicinity of the gap, thereby improving the recording density and permitting the manufacture of a thin film magnetic head adaptable to a higher recording density in future.
The NiFe alloy is formed within the above-described composition range, and thus the crystal can densely be formed, thereby suppressing surface roughness of the film plane and improving the corrosion resistance of the thin film magnetic head.
Instead of the above soft magnetic film, a soft magnetic film presented by the composition formula Ni1-XFeX may be used, in which the average crystal grain diameter is 130 xc3x85 to 175 xc3x85, and the Fe composition ratio X is in the range of 70% by mass to 90% by mass.
In the NiFe alloy according to the second embodiment of the present invention, the Fe composition ratio and the average crystal grain diameter of the NiFe alloy are defined.
As described above, the saturation magnetic flux density Bs mainly depends upon the Fe composition ratio X, but a higher saturation magnetic flux density Bs can be stably obtained by further setting the average crystal grain diameter in an appropriate range.
In U.S. patent application Ser. No. 09/599,349 (U.S. Pat. No. 6,449,122), the Fe composition ratio X can be increased to 75% by mass which lies in the range of the Fe composition ratio X of the NiFe alloy according to the second embodiment of the present invention.
Although the range of the Fe composition ratio X of the present invention partially overlaps with that of U.S. Pat. No. 6,449,122, the present invention greatly differs from U.S. Pat. No. 6,449,122 in the crystal grain diameter. Namely, in the present invention, the crystal grain diameter is defined to 130 xc3x85 or more, while in U.S. Pat. No. 6,499,122, the crystal grain diameter is defined to 105 xc3x85 or less.
In the present invention, crystallization is possibly appropriately promoted to increase the crystal grain diameter, forming a dense crystal, as compared with the NiFe alloy of U.S. Pat. No. 6,499,122. As a result, in the present invention, the saturation magnetic flux density Bs of the NiFe alloy can be increased to 1.9 T or more, succeeding in effectively increasing the saturation magnetic flux density Bs.
In the present invention, coercive force can be suppressed to 553 (A/m) or less. The coercive force Hc possibly increases as the crystal grain diameter increases. However, in the present invention, the coercive force Hc little increases even when the crystal grain diameter increases, and the coercive force Hc of 553 (A/m) or less is a low value sufficiently used, for example, for a core material of a thin film magnetic head.
The possible reason why the coercive force Hc can be kept down even when the crystal grain diameter increases is that a crystal is densely grown. When the crystal is densely formed, the surface roughness of a film plane can be decreased, and in the present invention, the center line average roughness Ra of the film plane can be suppressed to 10 nm or less. In the present invention, the center line average roughness Ra is preferably 7 nm or less.
By using the NiFe alloy for the core layers and the pole layers of the thin film magnetic head, a magnetic flux can be concentrated in the vicinity of the gap, thereby improving the recording density and permitting the manufacture of a thin film magnetic head adaptable to a higher recording density in future.
The NiFe alloy is formed within the above-described composition range, and thus the crystal can densely be formed, thereby suppressing surface roughness of the film plane and improving the corrosion resistance of the thin film magnetic head.
In the present invention, the Fe composition ratio X is preferably 72.5% by mass or more. This can increase the saturation magnetic flux density Bs of the NiFe alloy to 1.95 T or more.
Also, the average crystal grain diameter is preferably 150 xc3x85 or more. This can securely increase the saturation magnetic flux density Bs of the NiFe alloy to 1.95 T or more.
In the present invention, the Fe composition ratio X is preferably 78% by mass to 85% by mass. This can increase the saturation magnetic flux density Bs of the NiFe alloy to 2.0 T or more.
In the present invention, the soft magnetic film is preferably formed by plating. By forming the soft magnetic film by plating, the thickness can be relatively freely changed to form the soft magnetic thick film.
A method of manufacturing a thin film magnetic head of the present invention, which comprises a lower core layer made of a magnetic material, an upper core layer opposed to the lower core layer with a magnetic gap provided therebetween at the surface facing a recording medium, and a coil layer for inducing a recording magnetic field in both core layers, comprises forming the upper core layer and/or the lower core layer by plating a NiFe alloy by an electroplating method using a pulsed current, wherein the Ni ion concentration of a plating bath is 6.6 g/l to 20 g/l, and the ratio of the Fe ion concentration to the Ni ion concentration is 0.15 to 0.36.
In the present invention, preferably, a lower pole layer is further formed to protrude above the lower core layer at a surface facing a recording medium, wherein the lower pole layer comprises the soft magnetic film.
A method of manufacturing a thin film magnetic head of the present invention, which comprises a lower core layer, an upper core layer, and a pole portion located between the lower core layer and the upper core layer and having a width dimension in the track width direction, which is defined to be shorter than the lower core layer and the upper core layer, comprises forming the upper pole layer and/or the lower pole layer by plating a NiFe alloy by an electroplating method using a pulsed current, wherein the pole portion comprises a lower pole layer continued from the lower core layer, an upper pole layer continued from the upper core layer, and a gap layer positioned between the lower pole layer and the upper pole layer, or an upper pole layer continued from the upper core layer and a gap layer positioned between the upper pole layer and the lower core layer, and the Ni ion concentration of a plating bath is 6.6 g/l to 20 g/l, and the ratio of the Fe ion concentration to the Ni ion concentration is 0.15 to 0.36.
In the present invention, preferably, the upper pole layer comprises the soft magnetic film formed by plating, and the upper core layer formed on the upper pole layer comprises a soft magnetic film having a lower saturation magnetic flux density Bs than the upper pole layer.
In the present invention, preferably, each of the core layers comprises at least a portion in contact with the magnetic gap, which comprises at least two magnetic layers, or each of the pole layers comprises at least two magnetic layers, the magnetic layer in contact with the magnetic gap comprising the soft magnetic film formed by plating.
In the present invention, the magnetic layer other than the magnetic layer in contact with the magnetic gap comprises a soft magnetic film having a lower saturation magnetic flux density Bs than the magnetic layer in contact with the magnetic gap.
As described above, in the present invention, the NiFe alloy is plated by the electroplating method using the pulsed current. In the electroplating method using the pulsed current, for example, a current control device is repeatedly turned on and off to provide a time to pass the current, and a blank time to pass no current. By providing the time to pass no current, the NiFe alloy film can be slowly formed by plating to reduce the deviation of the current density distribution at the time of plating, as compared with an electroplating method using a DC current. By the electroplating method using the pulsed current, the Fe content of the soft magnetic film can easily be controlled to increase the Fe content of the film, as compared with the electroplating method using the DC current.
In the present invention, the Ni ion concentration of the plating bath is set to 6.6 g/l to 20 g/l. In a conventional method, the Ni ion concentration is about 40 g/l, while in the present invention, the Ni ion concentration is lower than that value. As a result, the amount of Ni ions of the plating solution, which contact the surface of a cathode (the plated side) during deposition, can be decreased, thereby increasing the Fe content of the NiFe alloy due to the improved agitation effect.
As described above, in the present invention, the ratio of the Fe ion concentration to the Ni ion concentration is set to 0.15 to 0.36. Namely, in the present invention, not only the Ni ion concentration but also the Fe ion/Ni ion ratio is defined to increase crystallinity, permitting the formation of a dense crystal. In the present invention, the Ni ion concentration is decreased, and the concentration ratio is set to the above value, increasing the Fe content and the crystal grain diameter of the NiFe alloy. However, since the dense crystal can be formed, a high saturation magnetic flux density Bs can be stably obtained, and coercive force Hx can be decreased. Furthermore, surface roughness can be decreased, and membrane stress can also be decreased.
By using the above-described plating bath, the NiFe alloy film having a Fe composition ratio of 76% by mass to 90% by mass, or a Fe composition ratio of 70% by mass to 90% by mass, and an average crystal grain diameter of 130 xc3x85 to 175 xc3x85 can be produced with high reproducibility.
In the present invention, preferably, the Ni ion concentration is 10 g/l or more, and the Fe ion concentration/Ni ion concentration ratio is 0.2 to 0.35.
In the present invention, preferably, the Ni ion concentration is 10 g/l or less, and the Fe ion concentration/Ni ion concentration ratio is 0.15 to 0.36.
In the present invention, saccharin sodium is preferably mixed with the plating bath of the NiFe alloy. Saccharin sodium (C6H4CONNaSO2) has the function as a stress relaxant, and the membrane stress of the NiFe alloy can be decreased by mixing saccharin sodium.
In the present invention, 2-butine-1,4-diol is preferably mixed with the plating bath. This can suppress coarsening of the crystal grains of the NiFe alloy plated to decrease the crystal grain diameter, thereby causing less voids between the crystal grains and suppressing surface roughness of the film plane. By suppressing surface roughness, the coercive force Hc can be decreased.
In the present invention, sodium 2-ethylhexyl sulfate is preferably mixed with the plating bath. Therefore, hydrogen produced in the plating bath is removed by sodium 2-ethylhexyl sulfate serving as a surfactant to prevent adhesion of hydrogen to the plated film, suppressing surface roughness.
Although sodium lauryl sulfate may be used instead of sodium 2-ethylhexyl sulfate, sodium 2-ethylhexyl sulfate produces less bubbles in mixing with the plating bath, and thus a large amount of sodium 2-ethylhexyl sulfate can be mixed with the plating bath, permitting the appropriate removal of hydrogen. By adding sodium 2-ethylhexyl sulfate, the membrane stress of the NiFe alloy can also be decreased.